In an open cut mine, bulk dozer push can be one of the most cost-effective methods of moving overburden. Under the right application, the unit cost of dozer push sits somewhere between a dragline and truck/shovel excavation. So, if geotechnical conditions are favourable and the dozer fleet is sufficient, dozer push should be considered to replace some of the truck/shovel prime. Dozer push can also be used to replace dragline prime. This is because it can speed up the linear progression of the dragline – which in many cases will lower the dragline unit cost rate and increase coal uncovery.
So how do you get the most out of your fleet? As with everything else, you need to understand your cost drivers. For Bulk Dozer Push, these are:
- Push Distance – Dozers are more cost effective over shorter push distances.
- Push grade – Downhill push uses gravity assist, uphill push reduces carry capacity.
- Material – Dozer’s don’t operate well with blocky material. Improve you blast fragmentation and your dozer’s will shine! It’s also important to remember material swell is variable throughout the blast profile, so as dozers get lower in the blast profile, the material will tend to get blockier and make the dozers less productive.
- Training – Operator competency has a significant impact in the overall production rate of the push. Improving their understanding of the pivot point and getting them to work together can make a huge impact on the fleet performance.
On the other hand, for Truck/Shovel the cost drivers are:
- Haul distance – Increased fuel consumption, increased number of trucks required to maintain excavator productivity.
- Elevation – Increased fuel consumption, wear and tear on truck, reduced travel speed.
- Productivity – Cost is impacted by a combination of hangtime, queue time and payload.
So, what is the pivot point? The pivot point is the point where the blast profile intersects the final lowwall. Dozers aim to work in a way in which they are cutting on highwall side of pivot point and filling on the lowwall side.
How can I optimise the dozer push design? This is case specific – though generally speaking, dozing below the pivot point will increase the amount of material being handled by the dozer but will generally result in less spoil room for bulk doze. On the other hand, raising the pivot point will increase the spoil room available for bulk dozer push but will introduce dozer rehandle to the next process.
To get the best-case scenario, the goals of the operation and the entire excavation sequence needs to be considered. By understanding the cost impacts on the next process, you may find maximising dozer push may not be the most cost-effective solution. For example, it may be more cost effective to raise the pivot point of the dozer push and take the dozer-rehandle using a truck and shovel fleet.
In addition to this, there may be opportunity to reduce operating costs by reviewing the prime material allocation. In the example below, increasing dozer prime movement improves coal uncovery and results in a decrease in the operating cost.
Click here if you would like to know more or think your operation could benefit from a Review of Mine Plan or Dozer Push Optimisation Study. MEC Mining would love to talk to hear from you!